Initially I wanted to install it into my existing slim PC case, which can be fitted into a small size travel luggage - but after ordering the PSU (my mistake that I didn't check the size) and liquid cooler (also didn't fit in) - I've got to settle with the current case. The slim case would have been easier to carry with one arm.

Just a suggestion that may or may not fit your recording lifestyle. In your case ( no pun intended) Albert you opted for a mini build.
 
My suggestion to anyone who does location recording is this: If at all possible use a laptop for capturing the rough tracks. Take the tracks back to your more powerful PC and do your editing and deep processing on it. 
 
If you need lot's of horsepower on location then this won't work. I think in some cases ( once again no pun intended) a person has plenty of computer in an average laptop to do the capture.
 
AND I'm going to contradict myself here- Some laptops are plenty powerful to capture a band including all the drum mics AND do the processing.
 
Just food for thought, might be junk food to you or maybe not.